In the early 1970's it became increasingly popular to market milk in plastic bags or pouches. Individually, these pouches would contain a quart or liter of milk for convenient house-hold dispensing. For market distribution, it was found desirable to sell multiple numbers of such pouches, preferably three, in a single outer bag or carrying sack. This second outer sack also reduces the risk that the inner pouches will be punctured, and if they are, serves to contain, at least partially, such leakage as may occur.
Lieberman U.S. Pat. No. 3,698,153 describes a very successful design for placing multiple pouches into a carrying sack. This design is now in broad use in North America.
Two important considerations in this field are speed and reliability. Speed is important for maximizing the output of a dairy in terms of the daily volume of milk shipped. The subject bagger places significant limits on production capacity because it accepts pouches linearly, and dispenses multiple pouch containing sacks downstream at a rate that is a proportionally reduced factor of the input speed of the pouches. Thus exiting sacks containing three pouches need merely be conveyed-away, and further processed, at one-third the incoming speed of the pouches.
Upstream from the bagger, milk can be fitted into pouches by multiple pouch-filling machines. With only one exit conveyor for a bagging station, it is apparent that the achievement of high speed at such bagging station is a critical objective.
Reliability is the second key factor in such an operation. If pouches or sacks break or get hung-up on conveyors, the entire line must be stopped. Unfortunately, experience has shown that as speed increases, reliability falls.
Existing pouch baggers can, with reasonable reliability, achieve packaging rates of about 100 pouches per minute. It is an object of this invention to increase this rate, without a significant loss in reliability.
The Lieberman machine receives pouches from an input conveyor, distributing them into a hopper with three sections. Adjustable chutes positioned between the two central sections consecutively direct pouches into each of the three sections or compartments. While this occurs, a trap door beneath the sections retains the pouches in position.
When all three compartments in the hopper are occupied, the trap door swings open. A series of plastic outer sacks or bags in a flattened state are hung next to the trap door. A flow of air from jets opens the top of the most proximate sack so that one of its upper edges lies in the path of the trap door as it swings open.
The opening of the trap door carries this upper first edge of the sack with it, exposing the opened sack as the pouches commence to fall therein.
The displaced edge of the sack is held open in known machines by the rear face of the trap door, held in a pinching-like manner against a contact or pinching plate that is supported on a frame. This prevents the free, upper edge of the sack from being carried immediately downwards by frictional drag arising from the descending pouches. When the pouches strike the bottom of the sack, their weight causes both of the upper edges of the sack to tear loose from their retaining means.
The filled sack then falls onto an exit conveyor for transport to the next station.
The pinching plate in known machines is sometimes loosely mounted to permit a slight vertical displacement, resisted by a spring. This freedom of movement has been found to reduce the incidence of premature release of the pinched edge. However, such failures are not uncommon with the existing design particularly when operated at higher speeds.
Air jets are used to initially open the top of the sack and move the free upper edge of the opening into the path of the trap door. It has been found that excessive airflow can, however, cause this edge to flutter, occasionally resulting in the failure of the trap door to engage with the free edge, and carry it to the pinching plate.
The flattened sacks are fed into the bagger by hanging them as a layered bundle on a pair of support rods that pass through a pair of holes formed in an upper, extended panel located as an extension to one of the upper ends of each sack. When the pouches fall into place the holes in this upper panel are torn open by the added weight, permitting the sack to fall.
Various systems exist for advancing the sacks along the rods as they are consumed. These include spring loaded arms that press against the sack. The Lieberman patent shows a plate with a handle hanging from an angled support shaft positioned above the mass of sacks. This plate exerts a constant force that serves to resist any tendency for the sacks to travel backwards, away from the trap door. No known system, however, provides a controlled pressure that varies with the number of sacks being advanced and is free of excess mechanical complexity and operates as effectively as that hereinafter described.
In existing machines the sacks containing bagged pouches are dropped directly onto a conveyor. This necessitates a clear gap sufficient for the weight of the pouches to tear the sacks loose from their support rods. The consequence is that a sack experiences a sharp, jerked acceleration when the weight of the pouches commences to tear the upper panel on the sack. This can cause uneven tearing and the consequent rotation of the sack into an inappropriate orientation when it becomes deposited on the conveyor. If the misalignment is serious, the production flow may have to be halted.
A means to reduce the incidence of such misalignments is desirable, and is accordingly an object of this invention.
A further failure of existing machines when run at the upper limit of their operational speed is that the first compartment of the hopper to be filled may become occupied by an entering pouch while the trap door is still in the course of closing (after release of the previous sack). This, on occasion, will prevent the trap door from closing. This problem exists only with respect to the first pouch to enter the hopper because the inflow of pouches is continuous, and the first pouch of the next series is following directly behind the last pouch of the previous series.
One solution is to increase the speed of closing of the trap door. However, this is noisy and stressful on components. The other solution of slowing down the infeed conveyor is also unsatisfactory.
As this phenomena places a limit on the rate of delivery of pouches to the hopper, an improvement to prevent interference between the first pouch and the trap door is clearly desirable.
These concerns all are directed to the problems of increasing the speed of operation of such a bagging machine, while maintaining reliability. This is the objective of the invention described hereafter.
The invention in its general form will first be described, and then its implementation in terms of specific embodiments will be detailed with reference to the drawings following hereafter. These embodiments are intended to demonstrate the principle of the invention, and the manner of its implementation. The invention in its broadest and more specific forms will then be further described, and defined, in each of the individual claims which conclude this Specification.